Communicable disease-causing organisms can be present at very high cell densities in the feces of infected humans and animals and water that is contaminated with sewage or fecal wastes poses a serious threat to human health.
There are presently available different methods for testing the sanitary quality of water. These methods include monitoring for indicator bacteria which are naturally present at high levels in the feces of humans and animals but which are not found in unpolluted or potable water supplies.
A primary drawback of most existing tests to determine the presence of sewage is that they are not specific to locating indicator bacteria of fecal origin, but rather also indicate other strains which do not necessarily originate in the intestines of warm-blooded animals, nor do they always come from man. Two commonly used bacterial indicator tests for determining the sanitary quality of water are the total coliform and fecal coliform procedures. These tests, however, give positive reactions for a group of bacteria which may not have been derived from feces. Included in the total coliform group are certain strains which are generally not found in fecal material, such as Klebsiella, Enterobacter, Citrobacter genera which may be found in soils and on vegetation and which are infrequently isolated in feces and then only in a very small amount. The fecal coliform group, which is comprised principally of the bacterium Escherichia coli, and which is the predominant fecal coliform found in feces, does include to a very lesser extent Klebsiella and Enterobacter so that a test result showing the presence of fecal coliforms may or may not indicate fecal contamination and follow-up investigation is the only accurate method of verifying the test results.
There are presently available test procedures which do verify the presence of fecal discharge in a test sample based on the specific determination of E. coli. E. coli is a common and natural inhabitant of the intestines of humans and animals and is present at a cell density in the range of 10.sup.7 to 10.sup.8 cells per gram of feces. These test methods include the use of fluorogenic and chromogenic chemicals namely, 7-hydroxy-4-methylcoumarin-7-.beta.-D-glucuronide and p-nitrophenyl-.beta.-D-glucuronide. These chemicals, although highly selective of E. coli, do not produce results for easily enumerating or quantifying the amount of E. coli present in a test specimen. In particular, the former chemical, otherwise known as MUG, fluoresces, thus requiring the use of a fluorescent light for analysis. This fluorescent light can be subject to interference in a membrane filter test and may result in poor accuracy of enumeration. The latter chemical, also known as PNG, is again not suitable for the enumeration of distinct E. coli colonies as the colour which develops during bacterial growth is not retained within the colony, but rather spreads throughout the entire test specimen making it impossible to count individual colonies.